1. Field of the Invention
The present invention relates to a process for producing a laminated semiconductor substrate, such as an SOI (silicon on insulator) substrate, and more particularly, to a process for producing a laminated semiconductor substrate able to be used, for example, in the production of a three-dimensional IC (integrated circuit).
2. Description of the Related Art
An SOI has a structure comprising an insulating substrate and a single crystal semiconductor layer formed thereon.
A process for the formation of the conventional SOI structure is disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 60-144949. In this process, an SiO.sub.2 film is first formed on a single crystal silicon substrate, and predetermined portions of the SiO.sub.2 film are etched to form a plurality of openings.
Thereafter, a single crystal silicon film is grown on the SiO.sub.2 film by a lateral epitaxial growth according to the vapor phase growth process, through the use of the single crystal silicon substrate at portions exposed at these openings as a seed crystal.
Then, the single crystal silicon film present in the opening is locally oxidized by thermal oxidation through the use of the single crystal silicon substrate appearing at the openings as a seed crystal to form an SiO.sub.2 film on this portion, thus causing the single crystal silicon film to be isolated from the single substrate by the SiO.sub.2 film, whereby an SOI structure comprising a single crystal silicon film formed on an SiO.sub.2 film is formed.
The above-described conventional process for forming an SOI structure, however, has the following problems.
Specifically, single crystal silicon films grown by lateral epitaxy through the use of the single crystal silicon substrate present in two openings adjacent to each other as a seed crystal collide with each other on the SiO.sub.2 film, and a boundary is formed at the collided portions, and thereafter, the region near the boundary unfavorably comprises a polycrystal.
When a polycrystal region is present in the single crystal silicon film on which a device is formed, the device characteristics may become unstable due to a generation of a current leakage of other phenomenon.
Accordingly, an object of the present invention is to provide a process for producing a laminated semiconductor substrate wherein the whole semiconductor layer on the insulating substrate can form a single crystal SOI structure.